Re: [PATCH 6/9] mm/compaction: rename is_via_compact_memory to compaction_with_allocation_order

[Baolin Wang]

On 8/22/2023 9:51 AM, Kemeng Shi wrote:
> on 8/19/2023 8:14 PM, Baolin Wang wrote:
> > On 8/15/2023 8:04 PM, Kemeng Shi wrote:
> > > on 8/15/2023 4:58 PM, Baolin Wang wrote:
> > > > On 8/5/2023 7:07 PM, Kemeng Shi wrote:
> > > > > We have order = -1 via proactive compaction, the is_via_compact_memory is
> > > > > not proper name anymore.
> > > > > As cc->order informs the compaction to satisfy a allocation with that
> > > > > order, so rename it to compaction_with_allocation_order.
> > > > >
> > > > > Signed-off-by: Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx>
> > > > > ---
> > > > >     mm/compaction.c | 11 +++++------
> > > > >     1 file changed, 5 insertions(+), 6 deletions(-)
> > > > >
> > > > > diff --git a/mm/compaction.c b/mm/compaction.c
> > > > > index d8416d3dd445..b5a699ed526b 100644
> > > > > --- a/mm/compaction.c
> > > > > +++ b/mm/compaction.c
> > > > > @@ -2055,12 +2055,11 @@ static isolate_migrate_t isolate_migratepages(struct compact_control *cc)
> > > > >     }
> > > > >       /*
> > > > > - * order == -1 is expected when compacting via
> > > > > - * /proc/sys/vm/compact_memory
> > > > > + * compact to satisfy allocation with target order
> > > > >      */
> > > > > -static inline bool is_via_compact_memory(int order)
> > > > > +static inline bool compaction_with_allocation_order(int order)
> > > >
> > > > I know naming is hard, but this name is not good enough that can show the compaction mode. But the original one could.
> > > Yes, I agree with this, but name and comment of is_via_compact_memory may
> > > mislead reader that order == -1 is equivalent to compaction from
> > > /proc/sys/vm/compact_memory.
> > > Actually, we have several approaches to trigger compaction with order == -1:
> > > 1. via /proc/sys/vm/compact_memory
> > > 2. via /sys/devices/system/node/nodex/compact
> > > 3. via proactive compact
> >
> > They can all be called proactive compaction.
> I have considered rename to is_proactive_compaction. But "proactive compaction"
> in comments of compaction.c mostly implies to compaction triggerred from
> /proc/sys/vm/compaction_proactiveness. So "proactive compaction" itself looks
> ambiguous...
> > > Instead of indicate compaction is tirggerred by compact_memocy or anything,
> > > order == -1 implies if compaction is triggerrred to meet allocation with high
> > > order and we will stop compaction if allocation with target order will success.
> >
> > IMO, the is_via_compact_memory() function helps people better distinguish the compaction logic we have under direct compaction or kcompactd compaction, while proactive compaction does not concern itself with these details. But compaction_with_allocation_order() will make me just wonder why we should compare with -1. So I don't think this patch is worth it, but as you said above, we can add more comments to make it more clear.
> Sure, no insistant on this.
> Is it looks good to you just change comment of is_via_compact_memory to:
> We need do compaction proactively with order == -1
> order == -1 is expected for proactive compaction via:
> 1. via /proc/sys/vm/compact_memory
> 2. via /sys/devices/system/node/nodex/compact
> 3. /proc/sys/vm/compaction_proactiveness

Look good to me. Thanks.

> > > > >     {
> > > > > -    return order == -1;
> > > > > +    return order != -1;
> > > > >     }
> > > > >       /*
> > > > > @@ -2200,7 +2199,7 @@ static enum compact_result __compact_finished(struct compact_control *cc)
> > > > >             goto out;
> > > > >         }
> > > > >     -    if (is_via_compact_memory(cc->order))
> > > > > +    if (!compaction_with_allocation_order(cc->order))
> > > > >             return COMPACT_CONTINUE;
> > > > >           /*
> > > > > @@ -2390,7 +2389,7 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
> > > > >           cc->migratetype = gfp_migratetype(cc->gfp_mask);
> > > > >     -    if (!is_via_compact_memory(cc->order)) {
> > > > > +    if (compaction_with_allocation_order(cc->order)) {
> > > > >             unsigned long watermark;
> > > > >               /* Allocation can already succeed, nothing to do */